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1.
The theory that any two people in the world are connected in some way by no more than six people.
Using sexual contact as an example: when one has contact with another person, contact is effectively made with every person that person has come into contact with, and every person those people have come into contact with and so on.
by Bill Hlavac July 07, 2003
 
2.
The phenomenon that everyone is connected to everyone in some way.
by MoonKnight March 25, 2003